Bug at computing a free resolution.

[anna-lena.winz@…]

I get the following bug when computing the resolution of an ideal given as the kernel of a map:

ring R_sv = 0,(x(1),x(2)),dp;                                                                                                   
ideal ti_sv = 0;                                                                                                                
qring r_sv = std(ti_sv);                                                                                                        
ring R_s2v = 0,(z(1),z(2),z(3),z(4),z(5),z(6)),dp;
<^1-1*z(1)^1*z(5)^1,1*z(4)^2-1*z(1)^1*z(6)^1,1*z(5)^1*z(6)^1-1*z(3)^1*z(4)^1,1*z(5)^2-1*z(3)^1*z(6)^1;
qring r_s2v = std(ti_s2v);
ring R_sv_tensor_R_s2v = 0,(x(1),x(2),z(1),z(2),z(3),z(4),z(5),z(6)),dp;
ideal ti_sv = 0;
qring r_sv_tensor_R_s2v = std(ti_sv);
setring r_s2v;
map f = r_sv_tensor_R_s2v,1*z(2)^1,1*z(6)^1,z(1),z(2),z(3),z(4),z(5),z(6);
setring r_sv_tensor_R_s2v;
ideal sigma2 = kernel(r_s2v, f);
def L = res(sigma2,2);

Singular : signal 11 (v: 3160): current line:>> re=sres(std(m),i);<< Segment fault/Bus error occurred at ffff because of 10206 (r:1395233037)

Any help is much appreciated,

Best, Anna-Lena

[anonymous]

 > ring R_sv = 0,(x(1),x(2)),dp;
 > ideal ti_sv = 0;
 > qring r_sv = std(ti_sv);
 > ring R_s2v = 0,(z(1),z(2),z(3),z(4),z(5),z(6)),dp;
 <^1-1*z(1)^1*z(5)^1,1*z(4)^2-1*z(1)^1*z(6)^1,1*z(5)^1*z(6)^1-1*z(3)^1*z(4)^1,1*z(5)^2-1*z(3)^1*z(6)^1;
 > qring r_s2v = std(ti_s2v);
 > ring R_sv_tensor_R_s2v = 0,(x(1),x(2),z(1),z(2),z(3),z(4),z(5),z(6)),dp;
 > ideal ti_sv = 0;
 > qring r_sv_tensor_R_s2v = std(ti_sv);
 > setring r_s2v;
 > map f =
 r_sv_tensor_R_s2v,1*z(2)^1,1*z(6)^1,z(1),z(2),z(3),z(4),z(5),z(6);
 > setring r_sv_tensor_R_s2v;
 > ideal sigma2 = kernel(r_s2v, f);
 > def L = res(sigma2,2);
 Singular : signal 11 (v: 3160):
 current line:>>          re=sres(std(m),i);<<
 Segment fault/Bus error occurred at ffff because of 10206 (r:1395233037)
 please inform the authors
 trying to restart...

[Oleksandr]

Hi,

Sorry, but ti_s2v in R_s2v is missing in your code :(

could you please provide r_sv_tensor_R_s2v and the final sigma2?

[anonymous]

ring R_sv = 0,(x(1),x(2)),dp;
ideal ti_sv = 0;
qring r_sv = std(ti_sv);
ring R_s2v = 0,(z(1),z(2),z(3),z(4),z(5),z(6)),dp;
ideal ti_s2v = 1*z(6)^2-1*z(1)^1*z(3)^1,1*z(4)^1*z(5)^1-1*z(1)^1*z(3)^1,1*z(4)^1*z(6)^1-1*z(1)^1*z(5)^1,1*z(4)^2-1*z(1)^1*z(6)^1,1*z(5)^1*z(6)^1-1*z(3)^1*z(4)^1,1*z(5)^2-1*z(3)^1*z(6)^1;
qring r_s2v = std(ti_s2v);
ring R_sv_tensor_R_s2v = 0,(x(1),x(2),z(1),z(2),z(3),z(4),z(5),z(6)),dp;
ideal ti_sv = 0;
qring r_sv_tensor_R_s2v = std(ti_sv);
setring r_s2v;
map f = r_sv_tensor_R_s2v,1*z(2)^1,1*z(6)^1,z(1),z(2),z(3),z(4),z(5),z(6);
setring r_sv_tensor_R_s2v;
ideal sigma2 = kernel(r_s2v, f);
def L = res(sigma2,2);

I am sorry, this is the full version of the code. It is generated automatically by a script, that is why some of the monomials look a little odd.

[Oleksandr]

looks like the problem is in the qring with zero quotient ideal:

ring R_sv_tensor_R_s2v = 0,(x(1),x(2),z(1),z(2),z(3),z(4),z(5),z(6)),dp;
ideal sigma2 = x(2)-z(6),x(1)-z(2),z(5)^2-z(3)*z(6),z(4)*z(5)-z(6)^2,z(1)*z(5)-z(4)*z(6),z(4)^2-z(1)*z(6),z(3)*z(4)-z(5)*z(6),z(1)*z(3)-z(4)*z(5);;sigma2 = std(sigma2);
def L=sres(sigma2,2); // OK!

qring Q = std(0); // leads to the BUG!

ideal sigma2 = x(2)-z(6),x(1)-z(2),z(5)^2-z(3)*z(6),z(4)*z(5)-z(6)^2,z(1)*z(5)-z(4)*z(6),z(4)^2-z(1)*z(6),z(3)*z(4)-z(5)*z(6),z(1)*z(3)-z(4)*z(5); sigma2 = std(sigma2);
def L=sres(sigma2,2); // BUG HERE!!!

[hannes]

fixed with bbcf7c800783ddc7d734be98c9fe0fc401e65d9e (sw) and 469b209cf000191a0f7ca6857826bfd55dbdaf85 (master)

see ​https://github.com/Singular/Sources/commit/bbcf7c800783ddc7d734be98c9fe0fc401e65d9e

[kroeker@…]

The commit does not contain a corresponding regression test.

Was a test added later?

[hannes]

please do not report nonsense: try "git log" and search for 587

[anonymous]

please do not report nonsense: try "git log" and search for 587

ok, a corresponding test was added in commit 0929ddc2c6615bd5e6fc2fcc07f26b85bdee0be9